Chopped ends http://www.ecfibreglasssupplies.co.uk/p-770-chopped-strands-6-mm.aspx

Here you go - http://www.cfsnet.co.uk/acatalog/CFS_Catalogue__Chopped_Strands_399.html

Make a paste and apply into corners with mixing stick.

Yep. If you can get it, loose strand is better than mat. Just simpler and easier to use. But of course you can just pull apart mat and do the same job. 

so best you suggest chopped frp?

Silica is good for increasing the density of resin, but it doesn't give it strength like rovings do. It doesn't form a matrix, there is no way of transferring load. So really it is just thick resin behind the gelcoat, which is better than a void as voids can expand and blister the gelcoat with heat etc. But still, the gelcoat will chip easier than it would with rovings. 

as what we used is from sanding dust and mixing with resin becomes very hard like rock but gives also weight so that is not good. why not silica?

That's a great little tip.

most people are throwing small off cuts away but chopping them up then saving them in a bag till such a time is a great idea.

Better to use loose chop strand. So the same stuff that makes up chop strand mat, but not bound together. Like so:

so what you suggest to use any image or link on sharp edges for molds or pieces from mold.? Guy suggested silica to use?

You have to be careful about using fillers like that on sharp mould edges, you are better off using roving and really getting it into the corner. Fillers tend to chip out with repeated use of the mould. You want to keep fibers against your gel coat, not filler.